1. Field of the Invention
The present invention relates generally to methods and apparatus for influencing living organisms by artificial magnetic fields. More particularly, the invention concerns a method and apparatus for controlling and harvesting fish using artificially induced magnetic fields. Specifically, the invention concerns method and apparatus for separating those tuna and dolphins which migrate in association.
2. Discussion of the Invention
For centuries the commercial harvesting of fish such as tuna, salmon, shrimp, bottom and mid-water fish and the like, has been accomplished using large nets. This type of fishing, as now practiced, is cumbersome, generally inefficient and often damaging to the ecology. Due to these facts, and because the public has become increasingly concerned with protecting the environment, the techniques used by commercial fishermen in trawl and seine net fishing has come under close scrutiny. Of particular concern is the needless killing of dolphin during commercial tuna fishing. When fishing for dolphin-associated tuna, the entire school of dolphins is typically encircled by a very large seine net. In such cases, the net not only captures the tuna which swim beneath the dolphins, but also frequently captures the dolphins which, being mammals, swim in the top surface layers of the water. The result is the incidental death of large numbers of dolphin by drowning.
In an attempt to avoid the problems inherent in net fishing, considerable effort has been devoted to alternate methods for harvesting fish. In this vein, there has been considerable experimentation with the reaction of living organisms, and particularly fish, to external stimuli such as sound, bubble screens, olfaction, chemoreception, light and predator and prey vocalizations. This experimentation has clearly shown that these stimuli are not particularly effective in eliciting repeatable responses of fish. On the other hand, clear evidence exists that fish will, in fact, respond to an artificial electric field. For example, controlled experiments have shown that fish can be attracted to the anode of an electrode array formed by two or more electrodes arranged to establish an artificial electric field in either fresh or sea water. However, because sea water is highly conductive, very large power requirements are necessary to establish electric fields of any magnitude.
While fish, both individually and in groups, clearly respond to electric fields, the very large power requirements necessary, the complexity of equipment design and the inordinately high costs associated with this technique have largely prevented widespread commercial application of electrofishing at sea. By way of example, in salt water with average conductivity, a 100 kilowatt source will produce a meaningful electrical effect within a range of only about five meters for smaller fish and about ten meters for larger fish. An extension of the fishing range to about twenty meters would require a source of about 1.6 megawatts. These disadvantages are not eliminated by the use of pulsed currents. Working range diameters significantly larger than twenty meters cannot be economically achieved with present technology. This is principally due to the substantial nonuniformity of the artificial electric field in the open sea and also due to the fact that the strength of the electric field decreases as the inverse square of the distance between the source and the point of observation.
In light of the drawbacks inherent in electrofishing and in view of the fact that the intensity of an artificial magnetic field produced, for example, by a long terminally grounded, electrically energized, insulated wire source varies only as the inverse first power of the distance from the source to the point of observation, the present inventor has turned his focus away from electrofishing and toward the use of magnetic fields in fishing operations. In this regard, there exists ample evidence that magnetic material is present in many living organisms such as algae, honeybees, sea turtles and in certain birds and fish, including tuna, dolphin (which are mammals, but herein are referred to broadly as "fish") and salmon. This magnetic material, which is also present in humans, forms permanent magnetic centers that provide a "compass sense" which enables varying degrees of orientation within the natural geomagnetic field. Experience has shown that any living organism that possesses this "compass sense" can be controlled within definite ranges by an external, artificially-induced magnetic field of sufficient magnitude to overcome this "compass sense" or sensitivity of the organism to variations in the natural geomagnetic field.